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  • Author or Editor: Robert Schutzki x
  • Journal of the American Society for Horticultural Science x
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Responses of Magnolia ×soulangiana (Soul.-Bod.) `Jane' (`Jane' saucer magnolia) to consecutive short term pretransplant drought stresses and recovery after transplanting were evaluated beginning October 1997 and June 1998. Plants were subjected to one (mild) or two (moderate) 3-day drought stress periods or a two 3-day and one 4-day (severe) drought stress period, each separated by two rewatering periods over 24 hours. One day after each stress period, plants were transplanted into the field and well watered to monitor recovery from stress. Plant response was determined by measuring whole-plant CO2 assimilation, leaf gas exchange (CO2 assimilation, transpiration, stomatal conductance) and canopy growth throughout stress and recovery periods. Whole-plant and leaf CO2 assimilation were lower for the stressed treatments for most of the measurements taken during stress in the fall and spring. After release from stress and transplanting, leaf CO2 assimilation returned to control levels for mild and moderate fall stresses within 2 to 3 d by the next measurement, while it was over 3 weeks until recovery from the severe stress. There was no difference in leaf gas exchange following release from stress and transplanting during the spring stress. More rapid defoliation occurred for the severe fall-stressed plants compared to the controls after release from stress in the fall. Flower number was reduced in spring for the fall-stressed plants. At termination of the experiment, the growth index was lower for severe fall-stressed plants but there were no differences for other fall stress treatments. There was no increase in growth for control or stressed plants for the spring experiment.

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Starch gel electrophoresis and principal component (PC) analysis were used to determine the levels of genetic variation and the relationship between morphology and geographic origin for Cornus florida (flowering dogwood) populations in a Michigan provenance plantation. The populations are representative of the species' geographic distribution, ranging from Texas to Georgia and north to Connecticut and Michigan. Allelic variation at 11 loci encoded by 5 enzymes was very low in comparison to other plant species. On average, populations displayed 1.16 alleles per locus, 9.89% of loci polymorphic, with an observed heterozygosity value of 0.048. Genetic identify values ranged from 0.961 to 1.00 and displayed no relationship with geographic origin. While the isozyme analysis revealed little genetic variation, the PC analysis revealed a considerable amount of morphological variation. Most variation (83.3%) in leaf and flower bud morphology was explained by three PCs. Leaf characters revealed no relationship with geographic origin. However, flower bud size and number of florets decreased with changes in latitude from northern, central, and southern populations, respectively. The relationship between flower bud size and latitude suggests an adaptive response to photoperiod throughout the species' geographic range.

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